It is generally known that salts of the twelve-vertex carborane anion CB11H12−(I) serve as starting materials for the preparation of partially and fully substituted anions of the type CB11XnH(12−n)− (II, where the substituents X need not be the same). The latter are of considerable interest as relatively inert and weakly nucleophilic anions for applications including, among others, incorporation in catalysts for olefin polymerization, incorporation in lithium cation battery electrolytes, and incorporation in radioactive waste treatment materials. The most common choices of substituent X for such applications are X=halogen, X=alkyl, and X=halogenated alkyl, e.g. trifluoromethyl.
Carborane anions, such as II, are described in U.S. Pat. No. 5,731,470, which is incorporated by reference in its entirety herein. This patent describes synthesis of these anions (II) from the corresponding unsubstituted anion (I). The patent also discusses the use of carborane anions in batteries and electrochromic displays.
Until the present time, the high cost of the starting material, CB11H12−, has discouraged commercial use of these highly promising anions. As far as we are aware, this starting material is at present sold commercially by only one company (Katchem Ltd., Prague, Czech Republic), and is very expensive. Currently the anion is produced from an expensive precursor, decaborane, in three steps; the synthesis is difficult to scale up and is performed in small batches.
The present invention provides a method for making unsubstituted anions (I) and related unsubstituted and monosubstituted carborane anions at significantly lower cost. The new synthetic method provided makes the use of these anions, and substituted anions, such as II, practical for commercial applications.